Interpretive Summary: More soybeans are produced than any other legume crop in the world. Soybean seed have value for their composition that is high in protein and oil. The soybean seed is mainly comprised of two large storage organs called cotyledons where the protein and oil is stored. The composition of all seeds is comprised of stored reserves that generate the energy and nutrition required for germination and the support of a new seedling. Seed composition is related to seed vigor and seedling growth so it is important to understand how the stored reserves are digested and moved from the cotyledons to support germination and seedling growth. We studied the five fatty acids in soybean cotyledons that comprise the oil fraction of the cotyledon using near-infrared (NIR) spectroscopy and developed an NIR method for complete fatty acid profiling of soybean cotyledons. This research is important because soybean breeders and biotechnologists are targeting specific changes to enhance the composition of soybean seed for new food, feed, and industrial uses. Our NIR method provides a fast, accurate, and inexpensive technique for determining fatty acid composition of a small 250-mg sample, a typical limitation when studying soybean cotyledons.

Technical Abstract:
Genetically improved soybean grain often contains altered fatty acid profiles. Such alterations can have deleterious effects on seed germination and seedling development, making it necessary to monitor fatty acid profiles in follow-up physiological studies. The objective of this research was to quantify the five fatty acids in soybean (Glycine max) cotyledons using near-infrared (NIR) spectroscopy. Soybean cotyledon samples were dried, ground, and scanned with visible and NIR radiation from 400 to 2500 nm, and reflectance was recorded. Samples were also analyzed by gas chromatography (GC) for palmitic, stearic, oleic, linoleic, and linolenic acids and total oil; GC data expressed as actual concentration and proportion of total oil were regressed against spectral data to develop calibration equations. Equation statistics indicated that four of the five fatty acids could be predicted accurately by NIR spectroscopy; the fifth fatty acid could be determined by subtraction. Principal component analysis revealed that most of the spectral variation in this population was due to chlorophyll absorbance in the visible region. Therefore, the spectra were trimmed to include the NIR region only (1100-2500 nm), and a second set of equations was developed. Equations based exclusively on NIR spectra were as precise or more precise than those based on visible and NIR spectra. Principal component analysis and partial least squares analysis revealed that even after trimming, at least 90% of the spectral variation was unrelated to fatty acid, though variation from fatty acid was identified in the second and third principal components. This research provides an NIR method for complete fatty acid profiling of soybean cotyledons. Equations were achieved with NIR spectra only, so spectrophotometers that analyze both the visible and NIR regions are not needed for this analysis. In addition, equations were possible with a 250-mg sample, which is one-tenth the normal sample size for this analysis.